Method for improving thickness uniformity of deposited ozone-TEOS silicate glass layers

ABSTRACT

A method for depositing highly conformal silicate glass layers via chemical vapor deposition through the reaction of TEOS and O 3  comprises placing an in-process semiconductor wafer having multiple surface constituents in a plasma-enhanced chemical vapor deposition chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.09/935,833, filed Aug. 23, 2001, pending, which is a continuation ofapplication Ser. No. 09/548,491, filed Apr. 13, 2000, now U.S. Pat. No.6,297,175 B1, issued Oct. 2, 2001, which is a continuation ofapplication Ser. No. 09/222,565, filed Dec. 29, 1998, now U.S. Pat. No.6,107,214, issued Aug. 22, 2000, which is a continuation of applicationSer. No. 08/841,908, filed Apr. 17, 1997, pending.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to processes for depositing compounds bymeans of chemical vapor deposition and, more particularly, to processesfor depositing silicon dioxide layers using ozone andtetraethylorthosilane as precursor compounds.

[0004] 2. State of the Art

[0005] Doped and undoped silicon dioxides, which are commonly referredto as silicate glasses, are widely used as dielectrics in integratedcircuits. Although silicon dioxide possesses a tetrahedral matrix whichwill impart a crystalline structure to the material under proper heatingand cooling conditions, the silicon dioxides used as dielectrics inintegrated circuits are typically amorphous materials. This applicationuses the term “silicate glass” to refer to silicon dioxides depositedvia chemical vapor deposition (CVD), as the term encompasses materialscontaining not just silicon dioxide, but dopants and other impurities aswell.

[0006] Chemical vapor deposition of silicate glasses has become ofparamount importance in the manufacture of contemporary integratedcircuits. For example, silicate glass doped with both boron andphosphorous is widely used as an interlevel dielectric and as a gettermaterial for mobile sodium ions.

[0007] Chemical vapor deposition (CVD) of silicate glasses by thesemiconductor industry is most commonly accomplished by reactingtetraethylorthosilane (TEOS), silane or disilane with an oxidizer.Silane is typically reacted with diatomic oxygen (O₂) or nitrous oxide(N₂O) at a temperature of about 400° C. TEOS, on the other hand, isgenerally reacted with either O₂ or ozone (O₃). If a low reactiontemperature is desirable, the use of ozone permits a reduction in thereaction temperature to about half that required for 2. For the sake ofbrevity, glass layers deposited from the reaction of O₃ and TEOS shallbe termed “ozone TEOS glasses”. The reaction temperature may also bereduced for the TEOS-O₂ reaction by striking a plasma in the depositionchamber. Glasses deposited via this plasma-enhanced chemical vapordeposition (PECVD) method shall be referred to hereinafter as PECVD-TEOSsilicate glasses. The plasma generates highly reactive oxygen radicalswhich can react with the TEOS molecules and provide rapid depositionrates at much reduced temperatures.

[0008] Silane is used for the deposition of silicate glasses whensubstrate topography is minimal, as the deposited layers arecharacterized by poor conformality and poor step coverage. Silicateglasses deposited from the reaction of TEOS with O₂ or O₃ are being usedwith increasing frequency as interlevel dielectrics because thedeposited layers demonstrate remarkable conformality that permits thefilling of gaps as narrow as 0.25 μm. Unfortunately, the deposition rateof silicate glass formed by the reaction of TEOS and O₃ is highlysurface dependent. A particularly acute problem arises when thedeposition is performed on a surface having topographical features withnon-uniform surface characteristics. For example, the deposition rate isvery slow on PECVD-TEOS glass layers, considerably faster on silicon andon aluminum alloys, and faster still on titanium nitride, which isfrequently used as an anti-reflective coating for laser reflow ofaluminum alloy layers. A correlation seems to exist between the qualityand relative deposition rate of ozone-TEOS glass layers. For example,ozone TEOS glass layers that are deposited on PECVD-TEOS glass layershave rough, porous surfaces and possess high etch rates.

[0009] In U.S. Pat. No. 5,271,972 to K. Kwok et al., it is suggestedthat the surface sensitivity of ozone-TEOS glass layers deposited onPECVD-TEOS glass layers may be related to the presence of a hydrophilicsurface on the PECVD-TEOS glass layers. A hydrophilic surface on thePECVD-TEOS glass layer may be attributable to embedded elemental carbonparticles which are formed as the TEOS precursor gas is attached byoxygen radicals generated by the plasma. As elemental carbon particlesare characteristically hydrophilic, they repel TEOS molecules, which arecharacteristically hydrophobic, and interfere with their absorption onthe surface of the deposited layer. Thus, the poor absorption rate ofTEOS molecules on the surface of PECVD-TEOS glass results in slowlydeposited, poor-quality films. Experimental evidence indicates thatdeposition rates are low for hydrophilic surfaces and high forhydrophobic surfaces. For example, titanium nitride, being highlyhydrophobic, readily absorbs TEOS molecules on its surface, whichaccelerates the deposition reaction.

[0010] Given the surface-dependent variation in deposition rates, it isnot uncommon for ozone-TEOS glass layers to build up rapidly aroundaluminum conductor lines and much more slowly on PECVD glass layers onwhich the conductor lines are fabricated, thereby forming cavities oftear-drop cross section between adjacent conductor lines. FIG. 1 is across-sectional view which depicts the undesirable result obtained byconventionally depositing an ozone-TEOS layer 11 over aluminum conductorlines 12 which overlie an underlying PECVD-TEOS glass layer 113. Priorto patterning, the aluminum conductor lines 12 were covered with atitanium nitride layer which served as an anti-reflective coating duringa laser reflow operation. A titanium nitride layer remnant 14 is presenton the upper surface of each aluminum conductor line 12. A cavity 15having a teardrop-shaped cross section has formed between each pair ofaluminum conductor lines 12. Cavities in an interlevel dielectric layerare problematic primarily because they can trap moisture when thedeposited glass layer is subjected to a planarizing chemical mechanicalpolishing step during a subsequent fabrication step. The moisture, ifnot completely removed prior to the deposition of subsequent layers, cancorrode metal conductor lines during normal use and operation of thepart, or it may cause an encapsulated integrated circuit device torupture if the steam generated as the device heats up is unable toescape the package.

[0011] In U.S. Pat. No. 5,271,972, a technique is disclosed forimproving the film quality of ozone-TEOS glass layers deposited onPECVD-TEOS glass layers. The method involves depositing the underlyingPECVD-TEOS layer using high pressure and a high ozone-to-TEOS flow rate.For the last several seconds of the plasma-enhanced deposition process,a stepwise reduction in reactor power is carried out. It is claimed thatthis technique produces an interstitial silicon dioxide layer at thesurface of the PECVD-TEOS layer which greatly reduces the surfacesensitivity of subsequently deposited ozone-TEOS oxide layers.

SUMMARY OF THE INVENTION

[0012] This invention provides an alternative method for depositinghighly conformal silicate glass layers via chemical vapor depositionthrough the reaction of TEOS and O₃ and for minimizing surface effectsof different materials on the deposition process.

[0013] The entire method, which can be performed in a single clustertool or even in a single chamber, begins by placing an in-processintegrated circuit having multiple surface constituents in aplasma-enhanced chemical vapor deposition chamber. A “clean” silicateglass base layer that is substantially free of carbon particleimpurities on an upper surface thereof is then formed on the wafersurface in one of two ways.

[0014] The first way of forming the clean base layer employsplasma-enhanced chemical vapor deposition using TEOS and diatomic oxygengases as precursors to first deposit a “dirty” silicate glass base layerhaving carbon particle impurities imbedded on the upper surface. Glasslayers deposited via PECVD by the reaction of TEOS and O₂ tend to haveelemental carbon particles embedded therein. As these particles mayimpart hydrophilic surface characteristics to the deposited glass layerwhich may interfere with the subsequent deposition of dense,high-quality ozone-TEOS glass layers, the base glass layer is subjectedto a plasma treatment which involves flowing a mixture of anoxygen-containing diamagnetic oxidant, such as ozone or hydrogenperoxide or a combination of both, and diatomic oxygen gas into thechamber and striking an RF plasma at a power of 50-350 watts for aperiod of from 30-300 seconds. It is hypothesized that the plasmatreatment burns off the carbon particle impurities that are present onthe surface of the dirty silicate glass base layer, thereby reducing thehydrophilic surface characteristics. The plasma treatment also creates ahigh degree of surface uniformity on the PECVD-deposited O₂-TEOS glasslayer.

[0015] The second way of forming the base layer involves flowinghydrogen peroxide vapor and at least one gaseous compound selected fromthe group consisting of silane and disilane into the deposition chamber.As an optional step, the clean base layer formed via this second methodmay be subjected to a plasma treatment identical to that performed onthe dirty PECVD-deposited O₂-TEOS glass layer. This optional plasmatreatment step is performed merely to improve surface uniformity, notreduce hydrophilic surface characteristics.

[0016] Following the formation of the clean base layer, a final glasslayer is deposited over the PECVD-deposited glass layer using chemicalvapor deposition and TEOS and ozone as precursor compounds.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0017]FIG. 1 is a cross-sectional view of a portion of an in-processintegrated circuit which has been subjected to a conventional blanketdeposition of ozone-TEOS silicate glass;

[0018]FIG. 2 is a cross-sectional view of a portion of an in-processintegrated circuit identical to that of FIG. 1 following deposition of abase glass layer;

[0019]FIG. 3 is a cross-sectional view of the in-process circuit portionof FIG. 2 following plasma treatment;

[0020]FIG. 4 is a cross-sectional view of the in-process circuit portionof FIG. 3 following the deposition of a final ozone-TEOS glass layer;and

[0021]FIG. 5 is a flow chart summarizing the various steps of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0022] This invention is embodied in a process for depositing highlyconformal silicate glass layers via chemical vapor deposition throughthe reaction of tetraethylorthosilane (TEOS) and O₃. The entire process,which can be performed in a single cluster tool or even in a singlechamber, begins by placing an in-process semiconductor wafer in aplasma-enhanced chemical vapor deposition chamber. In a typical case,hundreds of integrated circuits are undergoing simultaneous fabricationon the wafer, and each integrated circuit has topography with multiplesurface constituents. FIG. 2 is a cross-sectional view which depicts asmall portion of an integrated circuit identical to that of FIG. 1. Aplurality of parallel aluminum conductor lines 12 overlies a silicondioxide layer 13. Each aluminum conductor line 12 is covered with atitanium nitride layer 14 which served as an anti-reflective coatingduring a laser reflow operation which preceded masking and etching stepswhich formed the conductor lines. Each of the different materials hasdifferent surface characteristics which affect the rate of depositionfor ozone-TEOS glass layers.

[0023] In order to eliminate surface characteristics, a “clean” silicateglass base layer is formed which completely covers all existingtopography. The base layer must be clean in the sense that its uppersurface is free of hydrophilic carbon particle impurities which wouldinterfere with the deposition of an ozone-TEOS final glass layer. Theclean base layer may be formed in one of two ways.

[0024] Referring now to FIG. 2, the first way involves depositing a“dirty” base silicate glass layer 21 on all constituent surfaces viaplasma-enhanced chemical vapor deposition (PECVD). The PECVD depositionof the base silicate glass layer 21 is performed in a deposition chamberin which a plasma is ignited formed from a mixture of TEOS, oxygen andan inert carrier gas such as helium or argon which transports TEOSmolecules to the chamber.

[0025] Deposition of the PECVD base silicate glass layer 21 is effectedwithin a plasma deposition chamber at a pressure within a range of about1-50 tort (preferably within a range of about 1-10 tort), an oxygen flowrate of about 100-1000 sccm, a carrier gas flow rate of about 100-1500sccm, and with an RF power density of about 0.7 watts/cm² to about 3.0watt/cm². The deposition temperature is maintained within a range ofabout 300 to 500° C., with a preferred temperature of about 375° C. Thisprocess is described in greater detail in U.S. Pat. No. 4,872,947, whichissued to Chang et al., and is assigned to Applied Materials, Inc. Thispatent is incorporated herein by reference.

[0026] A suitable CVD/PECVD reactor in which the present process can becarried out in its entirety is also described in U.S. Pat. No.4,872,947. Silicate glass layers can be deposited using standard highfrequency RF power or a mixed frequency RF power.

[0027] The base silicate glass layer 21 is deposited to an averagethickness within a range of about 100 to 1000 Å. The optimum thicknessis deemed to be approximately 500 Å. Although the deposition rate ofplasma-enhanced chemical-vapor-deposited oxide from TEOS and O₂ is moreeven on different surfaces than it is for ozone-TEOS oxide, it isessential that all surfaces are completely covered.

[0028] An untreated TEOS silicate glass layer deposited via aplasma-enhanced CVD process tends to have embedded elemental carbonparticles which are formed as the TEOS precursor gas is attacked byoxygen radicals generated by the plasma. These carbon particlesapparently impart hydrophilic surface characteristics to an untreatedbase silicate glass layer 21 which are most likely responsible for theuneven deposition rates observed during subsequent depositions of dense,high-quality PECVD ozone-TEOS glass layers. In order to reduce oreliminate such interfering surface characteristics, the dirty basesilicate glass layer 21 is subjected to a plasma treatment whichinvolves flowing a mixture of an oxygen-containing diamagnetic oxidantgas, such as ozone (O₃) or hydrogen peroxide (H₂O₂) or a combination ofboth, and diatomic oxygen (O₂) gas into the chamber and striking an RFplasma. A mixture of 4 to 15 percent O₃ or H₂O₂ in O₂ is admitted to thechamber at a flow rate of about 2,400 standard cc/min. The plasma issustained at a power density setting of 0.25 watt/cm² to about 3.0watt/cm² for a period of from 30-360 seconds. In order to preventetching of the deposited base silicate glass layer 21 and uncovering ofadditional impurity sites, a remote-source plasma generator is preferredover a parallel-plate reactor. The plasma treatment is represented byFIG. 3, which depicts a plasma cloud 31 which completely engulfs thein-process integrated circuit portion of FIG. 2, thereby exposing allsurfaces of the base silicate glass layer 21 to the oxygen plasma. It ishypothesized that the plasma treatment burns off impurities, such as thecarbon particles, which are present in the PECVD-deposited base silicateglass layer 21, thereby reducing or eliminating the hydrophilic surfacecharacteristics. The plasma treatment creates a high degree of surfaceuniformity on the PECVD-deposited base silicate glass layer 21.

[0029] Referring once again to FIG. 2, which may also be used torepresent the second method of forming a clean base silicate glass layer21 involves a non-plasma-enhanced chemical vapor deposition effected byflowing hydrogen peroxide vapor and at least one gaseous compoundselected from the group consisting of silane and disilane into thedeposition chamber. A clean silicate glass base layer having no imbeddedcarbon particle impurities is deposited. The reaction of hydrogenperoxide vapor with either silane or disilane is performed within atemperature range of about 0° C. to 40° C., at a chamber pressure ofless than about 10 torr, and at a flow rate maintained for silane ordisilane within a range of about 10 sccm to 1,000 sccm. The hydrogenperoxide is introduced into the deposition chamber in combination withat least one carrier gas selected from the group consisting of nitrogenand the noble gases. The hydrogen peroxide is picked up by the carriergas in a bubbler apparatus, and the flow rate of the carrier gas (withthe hydrogen peroxide) into the deposition chamber is maintained withina range of about 50 sccm to 1,000 sccm. In addition, the hydrogenperoxide may be introduced into the deposition chamber via liquidinjection using a liquid-flow controller in combination with avaporizer.

[0030] As an optional step, the clean base layer formed via this secondmethod may be subjected to a plasma treatment identical to thatperformed on the dirty PECVD-deposited O₂-TEOS glass layer. Thisoptional plasma treatment step is performed merely to improve surfaceuniformity, not reduce hydrophilic surface characteristics.

[0031] Referring now to FIG. 4, an ozone-TEOS silicate glass layer 41 isdeposited on top of the clean silicate glass base layer 42. As theprocesses required for the formation of the silicate glass base layer,the plasma treatment step, and the ozone-TEOS deposition step sharecertain parameters in common, the same chamber can be used for allprocess steps. For the plasma treatment step, the TEOS flow and theconcomitant carrier gas flow are terminated, plasma generationcontinues, and ozone is added to the still flowing O₂ gas. For theozone-TEOS deposition step, the TEOS flow is resumed and the O₂ and O₃ratios are adjusted as necessary. The ozone-TEOS deposition step isaccomplished by flowing TEOS, oxygen and ozone gases into the depositionchamber, which is maintained at a pressure greater than 10 torr, and,preferably, within a range of about 500 to 760 torr. Substratetemperatures are maintained within a range of about 300-600° C., andpreferably at a temperature of about 400° C. A dense, highly conformalozone-TEOS silicate glass layer 41 is deposited that rapidly fills inthe remaining gaps between the conductor lines 12. The ozone-TEOSsilicate glass layer 41 demonstrates a high degree of conformality upondeposition. Cavities present in ozone-TEOS silicate glass layersdeposited using conventional deposition methods are eliminated.

[0032] The present process is highly advantageous because deposition ofthe PECVD base silicate glass layer 21, plasma treatment of the basesilicate glass layer 21, and deposition of the ozone-TEOS silicate glasslayer 41 can be performed in sequence, in the same reaction chamber,requiring a minimum of changes in the reactor, and without having toremove the substrate from the reaction chamber between the varioussteps. Likewise, if the base silicate glass layer is deposited usinghydrogen peroxide and silane or disilane as precursors, all steps may beperformed within the same reaction chamber without having to remove thesubstrate from the chamber between the various steps.

[0033]FIG. 5 summarizes the various options of the process which is thesubject of this disclosure. The first major step, providing a “clean”silicate glass base layer 51, can be performed in two basic ways: thedirty deposition and cleaning route 52 using TEOS and O₂ as precursorgases for a PECVD deposition step 53 followed by a cleaning plasmatreatment step 54 involving O₂ and H₂O₂ and/or O₃, or the CVD route 55using silane or disilane and H₂O₂ as precursor gases in a CVD depositionstep 56 and, optionally, the plasma surface treatment of step 54. Thefinal step 57 is CVD deposition of a final glass layer using TEOS and O₃as precursor gases.

[0034] Various changes to the gas mixtures, temperature and pressure ofthe reactions are contemplated and are meant to be included herein.Although the ozone-TEOS glass deposition process is described in termsof only a single embodiment, it will be obvious to those having ordinaryskill in the art of semiconductor integrated circuit fabrication thatchanges and modifications may be made thereto without departing from thescope and the spirit of the invention as hereinafter claimed.

What is claimed is:
 1. A method of depositing silicate glass on asubstrate comprising: placing a substrate within a plasma-enhancedchemical vapor deposition chamber; providing a first gaseous mixturecomprising TEOS, oxygen, and at least one inert carrier gas to form afirst gaseous atmosphere in the plasma-enhanced chemical vapordeposition chamber; generating a plasma surrounding the substrate in theplasma-enhanced chemical vapor deposition chamber in the first gaseousmixture comprising TEOS, oxygen, and at least one inert carrier gas;depositing a silicate glass base layer on said substrate, said silicateglass base layer having carbonaceous impurities, at least some of saidcarbonaceous impurities being exposed on an upper surface of saidsilicate glass base layer; providing a second gaseous mixture comprisingoxygen and hydrogen peroxide to form a second gaseous atmosphere in saidplasma-enhanced chemical vapor deposition chamber; igniting a plasma insaid second gaseous atmosphere in said plasma-enhanced chemical vapordeposition chamber; contacting at least the upper surface of saidsilicate glass base layer with at least a portion of said plasma in saidsecond gaseous atmosphere in said plasma-enhanced chemical vapordeposition chamber comprising oxygen and hydrogen peroxide to convert aportion of said carbonaceous impurities on the upper surface of saidsilicate glass base layer to a gas; removing at least a portion of saidsecond gaseous atmosphere from said plasma-enhanced chemical vapordeposition chamber; preventing said carbonaceous impurities converted tothe gas from contacting said silicate glass base layer by removing saidcarbonaceous impurities from said plasma-enhanced chemical vapordeposition chamber; depositing a final glass layer on said upper surfaceof said silicate glass base layer by flowing a third gaseous atmospherecomprising TEOS and ozone into said plasma-enhanced chemical vapordeposition chamber.
 2. The method of claim 1, wherein said secondgaseous atmosphere is substantially removed from said plasma-enhancedchemical vapor deposition chamber prior to the deposition of the finalglass layer.
 3. The method of claim 1, wherein a thickness of saidsilicate glass base layer is within a range of about 100 to about 1000Å.
 4. The method of claim 1, wherein contacting said silicate glass baselayer is performed with the plasma generated with a power densitysetting of about 0.7 to about 3.0 watts/cm².
 5. The method of claim 1,wherein contacting said silicate glass base layer to the plasma lastsfor a period of about 30 to about 360 seconds.
 6. The method of claim 1,wherein said final glass layer is deposited at a temperature within arange of about 300 to about 600° C.
 7. The method of claim 1, whereinsaid final glass layer is deposited at pressures within a range of about10 to about 760 torr.
 8. The method of claim 1, wherein said substratecomprises at least a portion of a semiconductor wafer having incompleteintegrated circuits constructed thereon.
 9. The method of claim 1,wherein the depositing the silicate glass base layer, the contacting atleast the upper surface of said silicate glass base layer with at leasta portion of said plasma, and the depositing the final glass layer areall performed in a chemical vapor deposition chamber equipped having aplasma generator.
 10. A method of depositing silicate glass on a wafersubstrate comprising: placing a wafer substrate within a chemical vapordeposition chamber; providing a first gaseous mixture comprising TEOS,oxygen, and at least one inert gas to form a first gaseous atmospherefor the chemical vapor deposition chamber; generating a plasma using thefirst gaseous mixture to surround the wafer substrate in said chemicalvapor deposition chamber; depositing a silicate glass base layer havingan upper surface on the wafer substrate, said silicate glass base layerhaving exposed carbonaceous impurities at least on the upper surfacethereof; providing a second gaseous mixture comprising oxygen andhydrogen peroxide to form a second gaseous atmosphere; igniting a plasmain said second gaseous atmosphere; subjecting said silicate glass baselayer to at least a portion of the plasma ignited in said second gaseousatmosphere containing said second gaseous mixture comprising oxygen andhydrogen peroxide to convert at least a portion of said exposedcarbonaceous impurities to a gas; removing at least a portion of saidsecond gaseous atmosphere from said chemical vapor deposition chamber;removing at least a portion of said carbonaceous impurities converted tothe gas from contact with said silicate glass base layer; depositing afinal glass layer on said upper surface of said silicate glass baselayer by flowing a third gaseous atmosphere comprising TEOS gas andozone gas into said chemical vapor deposition chamber.
 11. The method ofclaim 10, wherein said second gaseous atmosphere is substantiallyremoved from said chemical vapor deposition chamber prior to thedeposition of the final glass layer.
 12. The method of claim 10, whereina thickness of said silicate glass base layer is within a range of about100 Å to about 1000 Å.
 13. The method of claim 10, wherein thesubjecting said silicate glass base layer comprises generating theplasma at power density setting of about 0.7 to about 3.0 watts/cm². 14.The method of claim 10, wherein the subjecting said silicate glass baselayer to the plasma lasts for a period of about 30 to about 360 seconds.15. The method of claim 10, wherein said final glass layer is depositedat a temperature within a range of about 300 to about 600° C.
 16. Themethod of claim 10, wherein said final glass layer is deposited atpressures within a range of about 10 to about 760 torr.
 17. The methodof claim 10, wherein said wafer substrate comprises at least a portionof a semiconductor wafer having incomplete integrated circuitsconstructed thereon.
 18. The method of claim 10, wherein the depositingsaid silicate glass base layer, the subjecting said silicate glass baselayer to at least a portion of the plasma, and the depositing said finalglass layer are all performed in a chemical vapor deposition chamberequipped with a plasma generator.